Respiratory diseases are a major cause of economic loss to the equine industry. Equine herpesviruses (EHV), equine influenza viruses (EIV), and the bacterium, Streptococcus equi are pathogens most often associated with infectious respiratory disease in horses. World wide, equine herpesviruses are major pathogens associated with morbidity in horses as a result of respiratory infection. Both equine herpesvirus type 1 (EHV-1) and type 4 (EHV-4) can cause respiratory disease. EHV-1 is also associated with abortions and neurological disease. Because of the high degree of mobility and the international nature of the equine industry, efficacious vaccines are needed to reduce the disease and control the spread of these pathogens.
A number of EHV vaccines are available commercially. None, however, generally is capable of conferring long lasting protection and most require frequent booster immunizations to achieve a significant level of protection against EHV infection. The most commonly recommended route of administration is via intramuscular injection, despite the respiratory system being a primary site of the infection in many instances. In addition, some of the commercial vaccines have been reported to cause undesirable side effects. A number of attempts at developing a recombinant vaccine for EHV have been reported. This approach, however, has not yet resulted in the introduction of a commercial recombinant vaccine which has achieved widespread acceptance.
Literature reports have consistently documented a high degree of variability in the capability of vaccines based on EHV-1 strains to provide cross protection against infection by EHV-4 strains. While vaccines based on EHV-4 strains have shown a greater propensity to provide some protection against both EHV-1 and EHV-4 strains, cross protection based on EHV-4 strains has also been reported to show variability.
There is accordingly a continuing need to develop additional vaccines capable of protecting horses against diseases associated with EHV-1 and/or EHV-4. It would also be advantageous to develop vaccine that is effective against EHV-1 and/or EHV-4 which could be administered via intranasally as well as via parenteral methods (e.g., intramuscularly, subcutaneously or intravenously).